Field of the Invention
The present invention relates to a complex protection device for blocking an abnormal state of current and voltage, and more particularly to a complex protection device for blocking an abnormal state of current and voltage in which a resistive element is configured in the form of a structure and thus the resistive element has enhanced durability and surface mounting technology suitable for automation can be utilized, and a plurality of resistive elements is configured in various resistances and sizes to be optimally designed for product characteristics.
Description of the Related Art
A non-return protection device, which operates by sensing overheating of equipment to be protected caused by overcurrent or in response to an abnormal increase in the ambient temperature, blocks an electric circuit through operation at a predetermined operating temperature for the safety purposes of the equipment. As an example, there is a protection device which heats a resistor by current of a signal for detecting an abnormality in equipment and operates a fuse unit by the generated heat. In a lithium ion secondary battery including a protection device, which includes a resistor generating heat in an abnormal state on a ceramic substrate and uses membrane resistance, the protection device prevents performance degradation or ignition due to dendrites formed on a surface of an electrode in an overcharge mode or prevents the battery from being charged to more than a predetermined voltage in a charge mode.
Korean Patent Application Publication No. 10-2001-0006916 discloses a protective element including: a low melting point metal body electrode and a heating element on a substrate; a low melting point metal body directly formed on the low melting point metal body electrode and the heating element; an inner sealing part formed on the low melting point metal body and formed of a solid flux to prevent surface oxidation of the low melting point metal body; and an outer sealing part or a cap that is formed outside of the inner sealing part and prevents a molten material from leaking to the outside of the protective element when the low melting point metal body is blown.
FIGS. 12A and 12B are a plan view and a sectional view of a conventional protection device including a fusible element (a low melting point metal body) on a resistor (a heating element). FIG. 13 is a photograph showing a state in which a fusible element is blown when overvoltage is applied to the conventional protection device.
Referring to FIGS. 12A and 12B, the conventional protection device includes a ceramic substrate 1, a paste-type resistor 2 formed on the ceramic substrate 1, and an insulator 3, a fuse terminal 4, a fusible element 5, and a case 6 that are sequentially stacked on the resistor 2. The fuse terminal 4 includes a connection portion 4a connected to a resistance terminal 8.
When current is supplied to the resistor 2, heat generated from the resistor 2 is dissipated via the resistance terminal 8 connected to the fuse terminal 4. That is, the heat generated from the resistor 2 is not uniformly supplied to the fusible element 5 such that a relatively low heat is supplied to a region thereof close to the connection portion 4a. 
Accordingly, as illustrated in FIG. 13, when the fusible element 5 is blown, a blown surface is non-uniform at opposite sides thereof, and thus an insulation distance of the region close to the connection portion 4a is very small, which results in low insulation stability.
In addition, the resistor 2 of the conventional protection device is formed by coating of a resistor paste formed of an inorganic-based binder or an organic-based binder and thus has reduced durability and does not exhibit sufficient time-lag characteristics to enable use at a high voltage.